Gas generation device and gas generation method

ABSTRACT

A control device receives an output signal from a liquid level sensor disposed in an anode chamber. This output signal indicates whether the liquid level of the electrolytic bath in the anode chamber is higher than a reference level. When the liquid level of the electrolytic bath in the anode chamber is higher than the reference level, the control device increases, by a prescribe value, the frequency of a compressor driving voltage that is generated in an inverter circuit. This increases the rotational speed of a motor in the compressor, increases the discharge pressure of hydrogen gas being discharged from the compressor, and decreases the pressure inside the cathode chamber. As a result, the liquid level of the electrolytic bath in the cathode chamber rises, and the liquid level of the electrolytic bath in the anode chamber falls below the reference level.

TECHNICAL FIELD

The present invention relates to a gas generation device and a gasgeneration method for generating a gas.

BACKGROUND ART

Conventionally, fluorine gas is used in the semiconductor manufacturingprocess and so on for material cleaning, surface modification, and otherpurposes. While the fluorine gas itself is used in some cases, a varietyof fluorine-based gases synthesized based on the fluorine gas, such asNF₃ (nitrogen trifluoride) gas, NeF (neon fluoride) gas, and ArF (argonfluoride) gas, may also be used in other cases.

For supplying fluorine gas stably in such sites, a fluorine gasgeneration device that generates fluorine gas by electrolysis of HF(hydrogen fluoride), for example, is used.

The fluorine gas generation device disclosed in Patent Document 1includes an electrolyzer. The interior of the electrolyzer is divided bya partition wall into a cathode chamber and an anode chamber. In theelectrolyzer, an electrolytic bath is formed with a KF-HF-based mixedmolten salt. A cathode is disposed in the cathode chamber, and an anodeis disposed in the anode chamber. HF is supplied through an HF supplyline to the electrolytic bath in the electrolyzer for electrolysis ofHF, whereby hydrogen gas is generated from the cathode and fluorine gasis generated from the anode in the electrolyzer.

At the top of the cathode chamber, an outlet for hydrogen gas isprovided. The hydrogen gas generated in the cathode chamber exits fromthe outlet and is discharged through a hydrogen gas line on the cathodeside. The hydrogen gas line is provided with an automatic valve and anHF adsorption column. Further, at the top of the cathode chamber, apurge gas inlet/outlet for supplying an inert gas into the cathodechamber is provided. This allows the inert gas to be supplied into thecathode chamber from an inert gas line through the purge gasinlet/outlet. The inert gas line is also provided with an automaticvalve.

At the top of the anode chamber, an outlet for fluorine gas is provided.The fluorine gas generated in the anode chamber exits from the outletand is discharged through a fluorine gas line. The fluorine gas line isprovided with an HF adsorption column and an automatic valve.Furthermore, on the fluorine gas line, a compressor unit is provided onthe downstream of the HF adsorption column and the automatic valve.Further, at the top of the anode chamber, a purge gas inlet/outlet forsupplying an inert gas into the anode chamber is provided. This allowsthe inert gas to be supplied also into the anode chamber from an inertgas line through the purge gas inlet/outlet. This inert gas line is alsoprovided with an automatic valve.

In each of the cathode chamber and the anode chamber, a liquid levelsensor is provided which detects the liquid level of the electrolyticbath in the corresponding chamber. The automatic valves disposed on thehydrogen gas line, the fluorine gas line, and the inert gas linesopen/close in accordance with the liquid levels of the electrolytic bathin the respective chambers detected by the liquid level sensors. As theautomatic valves open/close in response to the liquid levels detected bythe liquid level sensors, fluctuations in liquid level of theelectrolytic bath are restricted, and accordingly, fluctuations inelectrolysis conditions upon electrolysis of HF are restricted.

-   [Patent Document 1] JP 2004-52105 A

SUMMARY OF INVENTION Technical Problem

In order to restrict the fluctuations in liquid level of theelectrolytic bath, however, it is necessary to open/close the automaticvalves frequently. Particularly in the case where the liquid levelfluctuates constantly, the number of operations of opening/closing theautomatic valves per unit time increases. In this case, the lives of theautomatic valves are shortened, and the maintenance (replacement,repair, etc.) of the automatic valves needs to be performed frequently.This leads to an increase in maintenance cost.

An object of the present invention is to provide a gas generation deviceand a gas generation method capable of reducing the maintenance costwhile restricting the fluctuations in liquid level of the electrolyticbath.

Solution to Problem

(1) According to an aspect of the present invention, a gas generationdevice that generates a first gas and a second gas by electrolysisincludes an electrolyzer divided into a first chamber and a secondchamber and containing therein an electrolytic bath including a compoundto be electrolyzed, a first gas discharge path through which the firstgas generated in the first chamber is discharged, a second gas dischargepath through which the second gas generated in the second chamber isdischarged, a liquid level detector that detects a liquid level of theelectrolytic bath in the second chamber, a first pump having a motor andprovided on the first gas discharge path, a first inverter circuit thatgenerates a driving voltage to be applied to the motor of the firstpump, and a controller that controls the first inverter circuit, in thecase where the liquid level detected by the liquid level detector ishigher than a predetermined reference level, such that at least one ofan effective value and a frequency of the driving voltage being appliedto the motor of the first pump increases.

In this gas generation device, electrolysis of the compound included inthe electrolytic bath is carried out, so that a first gas is generatedin the first chamber and a second gas is generated in the secondchamber.

The first gas generated in the first chamber is discharged through thefirst gas discharge path by the first pump having a motor. The secondgas generated in the second chamber is discharged through the second gasdischarge path. The first pump operates as the driving voltage generatedby the first inverter circuit is applied to the motor.

The liquid level of the electrolytic bath in the second chamber isdetected by the liquid level detector. In the case where the detectedliquid level is higher than a reference level, the first invertercircuit is controlled such that at least one of the effective value andfrequency of the driving voltage being applied to the motor of the firstpump increases.

In this case, the rotational speed of the motor of the first pumpincreases, and the discharge pressure of the first gas by the first pumpincreases, so that the pressure inside the first chamber decreases. As aresult, the liquid level of the electrolytic bath in the first chamberrises, and also, the liquid level of the electrolytic bath in the secondchamber is adjusted to a level not higher than the reference level. Inthis manner, the fluctuations in liquid level of the electrolytic bathare restricted.

Further, in the first gas discharge path, the discharge pressure of thefirst gas is adjusted by changing the rotational speed of the motor ofthe first pump. This eliminates the need to adjust the dischargepressure of the first gas through the operations of opening/closing theopen/close valves. It is thus unnecessary to perform maintenance due tothe early deterioration of the open/close valves, and the number oftimes of maintenance work decreases. This results in a reduction of themaintenance cost of the gas generation device.

(2) The gas generation device may further include a first pressuredetector that detects a pressure inside the first chamber, and, in thecase where the liquid level detected by the liquid level detector is nothigher than the reference level, the controller may control at least oneof an effective value and a frequency of the driving voltage generatedby the first inverter circuit such that the pressure detected by thefirst pressure detector approaches a first target value.

In this case, the pressure inside the first chamber is detected by thefirst pressure detector. In the case where the liquid level detected bythe liquid level detector is not higher than the reference level, atleast one of the effective value and frequency of the driving voltagegenerated by the first inverter circuit is controlled such that thepressure detected by the first pressure detector approaches the firsttarget value.

This changes the rotational speed of the motor of the first pump, andchanges the discharge pressure of the first gas by the first pump,whereby the pressure inside the first chamber is adjusted to approachthe first target value. Accordingly, it is possible to restrict thefluctuations in pressure inside the first chamber, while restricting thefluctuations in liquid level in the second chamber.

(3) The gas generation device may further include a second pump having amotor and provided on the second gas discharge path, a second invertercircuit that generates a driving voltage to be applied to the motor ofthe second pump, and a second pressure detector that detects a pressureinside the second chamber, and the controller may control at least oneof an effective value and a frequency of the driving voltage generatedby the second inverter circuit such that the pressure detected by thesecond pressure detector approaches a second target value.

In this case, the second gas generated in the second chamber isdischarged through the second gas discharge path by the second pumphaving a motor. The second pump operates as the driving voltagegenerated by the second inverter circuit is applied to the motor.

The pressure inside the second chamber is detected by the secondpressure detector. At least one of the effective value and frequency ofthe driving voltage generated by the second inverter circuit iscontrolled such that the pressure detected by the second pressuredetector approaches the second target value.

This changes the rotational speed of the motor of the second pump, andchanges the discharge pressure of the second gas by the second pump,whereby the pressure inside the second chamber is adjusted to approachthe second target value. Accordingly, it is possible to restrict thefluctuations in pressure inside the second chamber, while restrictingthe fluctuations in liquid level in the second chamber.

(4) The gas generation device may further include a first pressuredetector that detects a pressure inside the first chamber, a second pumphaving a motor and provided on the second gas discharge path, a secondinverter circuit that generates a driving voltage to be applied to themotor of the second pump, and a second pressure detector that detects apressure inside the second chamber, and, in the case where the liquidlevel detected by the liquid level detector is not higher than thereference level, the controller may control at least one of an effectivevalue and a frequency of the driving voltage generated by the firstinverter circuit such that the pressure detected by the first pressuredetector approaches a first target value, and may also control at leastone of an effective value and a frequency of the driving voltagegenerated by the second inverter circuit such that the pressure detectedby the second pressure detector approaches a second target value that issmaller than the first target value.

In this case, the pressure inside the first chamber is detected by thefirst pressure detector. In the case where the liquid level detected bythe liquid level detector is not higher than the reference level, atleast one of the effective value and frequency of the driving voltagegenerated by the first inverter circuit is controlled such that thepressure detected by the first pressure detector approaches the firsttarget value.

This changes the rotational speed of the motor of the first pump, andchanges the discharge pressure of the first gas by the first pump,whereby the pressure inside the first chamber is adjusted to approachthe first target value. Accordingly, it is possible to restrict thefluctuations in pressure inside the first chamber, while restricting thefluctuations in liquid level in the second chamber.

Further, the second gas generated in the second chamber is dischargedthrough the second gas discharge path by the second pump having a motor.The second pump operates as the driving voltage generated by the secondinverter circuit is applied to the motor.

The pressure inside the second chamber is detected by the secondpressure detector. At least one of the effective value and frequency ofthe driving voltage generated by the second inverter circuit iscontrolled such that the pressure detected by the second pressuredetector approaches the second target value.

This changes the rotational speed of the motor of the second pump, andchanges the discharge pressure of the second gas by the second pump,whereby the pressure inside the second chamber is adjusted to approachthe second target value. Accordingly, it is possible to restrict thefluctuations in pressure inside the second chamber, while restrictingthe fluctuations in liquid level in the second chamber.

The second target value is smaller than the first target value. In thiscase, the pressures inside the first and second chambers are adjusted toapproach the first and second target values, respectively, andaccordingly, the pressure inside the second chamber becomes lower thanthe pressure inside the first chamber. This prevents the liquid level ofthe electrolytic bath in the first chamber from rising beyond the liquidlevel of the electrolytic bath in the second chamber.

(5) The gas generation device may further include a first open/closevalve provided on the first gas discharge path, and a second open/closevalve provided on the second gas discharge path, and the controller mayopen the first and second open/close valves in the case whereelectrolysis is carried out in the electrolyzer, and may close the firstand second open/close valves in the case where no electrolysis iscarried out in the electrolyzer.

In this case, the first and second open/close valves are opened whenelectrolysis takes place in the electrolyzer, while the first and secondopen/close valves are closed when no electrolysis takes place in theelectrolyzer.

This allows the first gas generated in the first chamber to bedischarged through the first gas discharge path when electrolysis iscarried out in the electrolyzer. This also allows the second gasgenerated in the second chamber to be discharged through the second gasdischarge path.

On the other hand, when no electrolysis is carried out in theelectrolyzer, the atmosphere outside the gas generation device isprevented from flowing into the first chamber through the first gasdischarge path. And the atmosphere outside the gas generation device isprevented from flowing into the second chamber through the second gasdischarge path.

(6) The first chamber may be a cathode chamber, and the second chambermay be an anode chamber.

In this case, the liquid level of the electrolytic bath in the anodechamber is detected by the liquid level detector. In the case where thedetected liquid level is higher than the reference level, the firstinverter circuit is controlled such that at least one of the effectivevalue and frequency of the driving voltage being applied to the motor ofthe first pump increases.

This increases the rotational speed of the motor of the first pump, andincreases the discharge pressure of the first gas by the first pump,whereby the pressure inside the anode chamber decreases. As a result,the liquid level of the electrolytic bath in the anode chamber rises,and also, the liquid level of the electrolytic bath in the cathodechamber is adjusted to a level not higher than the reference level.

(7) The second gas may be fluorine. In the second chamber where fluorineis generated, the liquid level of the electrolytic bath is likely torise at the time of electrolysis of the compound. Even in such a case,the fluctuations in liquid level of the electrolytic bath in the secondchamber are restricted, which ensures a stable supply of fluorine.

(8) According to another aspect of the present invention, a gasgeneration method for generating a first gas and a second gas byelectrolysis by using an electrolyzer divided into a first chamber and asecond chamber includes the steps of generating the first and secondgases in the first and second chambers, respectively, by applying avoltage to an electrolytic bath contained in the electrolyzer, anddischarging the first and second gases generated in the first and secondchambers through first and second gas discharge paths, respectively,controlling, by a first pump having a motor, the discharge of the firstgas through the first gas discharge path, detecting a liquid level ofthe electrolytic bath in the second chamber, applying a driving voltageto the motor of the first pump by a first inverter circuit, and in thecase where the detected liquid level is higher than a predeterminedreference level, controlling the first inverter circuit such that atleast one of an effective value and a frequency of the driving voltagebeing applied to the motor of the first pump increases.

In this gas generation method, a voltage is applied to the electrolyticbath contained in the electrolyzer, so that a first gas is generated inthe first chamber and a second gas is generated in the second chamber.The first and second gases generated in the first and second chambersare discharged through the first and second gas discharge paths,respectively. The discharge of the first gas through the first gasdischarge path is controlled by the first pump having a motor. The firstpump operates as a driving voltage is applied to the motor by the firstinverter circuit.

The liquid level of the electrolytic bath in the second chamber isdetected. In the case where the detected liquid level is higher than areference level, the first inverter circuit is controlled such that atleast one of the effective value and frequency of the driving voltagebeing applied to the motor of the first pump increases.

In this case, the rotational speed of the motor of the first pumpincreases, and the discharge pressure of the first gas by the first pumpincreases, so that the pressure inside the first chamber decreases. As aresult, the liquid level of the electrolytic bath in the first chamberrises, and also, the liquid level of the electrolytic bath in the secondchamber is adjusted to a level not higher than the reference level. Inthis manner, the fluctuations in liquid level of the electrolytic bathare restricted.

Further, in the first gas discharge path, the discharge pressure of thefirst gas is adjusted by changing the rotational speed of the motor ofthe first pump. This eliminates the need to adjust the dischargepressure of the first gas through the operations of opening/closing theopen/close valves. It is thus unnecessary to perform maintenance due tothe early deterioration of the open/close valves, and the number oftimes of maintenance work decreases. This results in a reduction of themaintenance cost of the gas generation device.

(9) The gas generation method may further include the steps of detectinga pressure inside the first chamber, in the case where the detectedliquid level is not higher than the predetermined reference level,controlling at least one of an effective value and a frequency of thedriving voltage generated by the first inverter circuit such that thedetected pressure inside the first chamber approaches a first targetvalue, controlling, by a second pump having a motor, the discharge ofthe second gas through the second gas discharge path, applying a drivingvoltage to the motor of the second pump by a second inverter circuit,detecting a pressure inside the second chamber, and controlling at leastone of an effective value and a frequency of the driving voltagegenerated by the second inverter circuit such that the detected pressureinside the second chamber approaches a second target value that issmaller than the first target value.

In this case, the pressure inside the first chamber is detected. In thecase where the detected liquid level is not higher than the referencelevel, at least one of the effective value and frequency of the drivingvoltage generated by the first inverter circuit is controlled such thatthe detected pressure approaches the first target value.

This changes the rotational speed of the motor of the first pump, andchanges the discharge pressure of the first gas by the first pump,whereby the pressure inside the first chamber is adjusted to approachthe first target value. Accordingly, it is possible to restrict thefluctuations in pressure inside the first chamber, while restricting thefluctuations in liquid level in the second chamber.

The second gas generated in the second chamber is discharged through thesecond gas discharge path by the second pump having a motor. The secondpump operates as the driving voltage generated by the second invertercircuit is applied to the motor.

The pressure inside the second chamber is detected. At least one of theeffective value and frequency of the driving voltage generated by thesecond inverter circuit is controlled such that the detected pressureapproaches the second target value.

This changes the rotational speed of the motor of the second pump, andchanges the discharge pressure of the second gas by the second pump,whereby the pressure inside the second chamber is adjusted to approachthe second target value. Accordingly, it is possible to restrict thefluctuations in pressure inside the second chamber, while restrictingthe fluctuations in liquid level in the second chamber.

The second target value is smaller than the first target value. In thiscase, the pressures inside the first and second chambers are adjusted toapproach the first and second target values, respectively, andaccordingly, the pressure inside the second chamber becomes lower thanthe pressure inside the first chamber. This prevents the liquid level ofthe electrolytic bath in the first chamber from rising beyond the liquidlevel of the electrolytic bath in the second chamber.

Advantageous Effects of Invention

According to the present invention, it is possible to reduce themaintenance cost while restricting the fluctuations in liquid level ofthe electrolytic bath.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing the configuration of a fluorinegas generation device according to an embodiment of the presentinvention.

FIG. 2 is a block diagram showing a part of a control system in thefluorine gas generation device in FIG. 1.

FIG. 3 shows graphs illustrating specific examples of liquid levelcontrol and pressure control.

FIG. 4 is a flowchart illustrating a series of processes of electrolysisusing the liquid level control and the pressure control.

FIG. 5 is a flowchart illustrating a series of processes of electrolysisusing the liquid level control and the pressure control.

FIG. 6 is a schematic diagram showing the configuration of the fluorinegas generation device according to another embodiment.

FIG. 7 is a schematic diagram showing the configuration of the fluorinegas generation device according to yet another embodiment.

DESCRIPTION OF EMBODIMENTS

A gas generation device and a gas generation method according to anembodiment of the present invention will now be described with referenceto the drawings. In the following embodiment, a fluorine gas generationdevice for generating fluorine gas will be described as an example ofthe gas generation device.

(1) Configuration of the Fluorine Gas Generation Device

FIG. 1 is a schematic diagram showing the configuration of the fluorinegas generation device according to an embodiment of the presentinvention. As shown in FIG. 1, the fluorine gas generation device 100includes an electrolyzer 1. The electrolyzer 1 is formed, for example,of Ni (nickel), Monel, pure iron, stainless steel, or other metal oralloy. The interior of the electrolyzer 1 is divided by a partition wall2 into a cathode chamber 3 and an anode chamber 4. The partition wall 2is made of Ni or Monel, for example.

In the electrolyzer 1, an electrolytic bath 5 of KF-HF-based mixedmolten salt is formed. A cathode 6 of Ni (nickel), for example, isdisposed in the cathode chamber 3, and an anode 7 of carbon with lowpolarizability, for example, is disposed in the anode chamber 4. As HF(hydrogen fluoride) is supplied through an HF supply pipe 10 to theelectrolytic bath 5 in the electrolyzer 1, electrolysis of HF takesplace. As a result, in the electrolyzer 1, hydrogen gas is primarilygenerated from the cathode 6 and fluorine gas is primarily generatedfrom the anode 7.

At the top of the cathode chamber 3, a cathode outlet 20 a is provided.Connected to the cathode outlet 20 a is an (upstream) end of a hydrogengas discharge pipe 20. The hydrogen gas generated in the cathode chamber3 exits from the cathode outlet 20 a and is discharged through thehydrogen gas discharge pipe 20. The hydrogen gas discharge pipe 20 hasan HF adsorption column 24, a control valve 21, a compressor 22, and acontrol valve 23 provided in this order from the upstream to thedownstream.

The HF adsorption column 24 is packed with NaF or the like. The HFadsorption column 24 serves to adsorb HF within a mixture of HF andhydrogen gas that is discharged from the cathode chamber 3. Thecompressor 22 is connected with an inverter circuit 22I. A drivingvoltage generated by the inverter circuit 22I is applied to thecompressor 22.

The hydrogen gas discharge pipe 20 has its downstream end connected, forexample, to an exhaust line in a factory. This allows the hydrogen gasdischarged from the cathode chamber 3 to be discharged through thefactory exhaust line.

At the top of the anode chamber 4, an anode outlet 30 a is provided.Connected to the anode outlet 30 a is an (upstream) end of a fluorinegas discharge pipe 30. The fluorine gas generated in the anode chamber 4exits from the anode outlet 30 a and is discharged through the fluorinegas discharge pipe 30. The fluorine gas discharge pipe 30 has an HFadsorption column 34, a control valve 31, a compressor 32, and a controlvalve 33 provided in this order from the upstream to the downstream.

The HF adsorption column 34 is packed with NaF or the like. The HFadsorption column 34 serves to adsorb HF within a mixture of HF andfluorine gas that is discharged from the anode chamber 4. The compressor32 is connected with an inverter circuit 32I. A driving voltagegenerated by the inverter circuit 32I is applied to the compressor 32.

The fluorine gas discharge pipe 30 has its downstream end connected, forexample, to a manufacturing line in a factory. This allows the fluorinegas discharged from the anode chamber 4 to be supplied, at apredetermined flow rate, to the factory manufacturing line or the like.

The cathode chamber 3 is provided with a pressure gauge PS1 thatmeasures the pressure inside the cathode chamber 3. The anode chamber 4is provided with a pressure gauge PS2 that measures the pressure insidethe anode chamber 4. The anode chamber 4 is further provided with aliquid level sensor 40 that detects the liquid level of the electrolyticbath 5 in the anode chamber 4.

The HF supply pipe 10 is provided with an automatic valve 11 and anorifice 12. In order to prevent the electrolytic bath 5 from beingsucked into the HF supply pipe 10, a control valve 13 is connectedbetween the hydrogen gas discharge pipe 20 and the HF supply pipe 10 onthe downstream of the orifice 12. It is noted that the HF supply pipe 10is provided with a pressure gauge (not shown).

In the present embodiment, the compressors 22, 32 are bellowscompressors that respectively include metal bellows and motors 22M, 23M(FIG. 2), which will be described later. During the operations of thecompressors 22, 32, the metal bellows are expanded/contracted by themotors 22M, 23M. The amounts of expansion/contraction as well as thecycles of expansion and contraction of the respective bellows at thattime can be adjusted so as to adjust the discharge pressures of thegases (hydrogen gas and fluorine gas) by the compressors 22, 23. It isnoted that the amount of expansion/contraction of the bellows refers tothe difference between the length of the bellows in the most expandedstate and the length of the bellows in the most contracted state.

(2) Control System in the Fluorine Gas Generation Device

A control device 90 includes a central processing unit (CPU) and amemory, or a microcomputer. The control device 90 controls theoperations of the elements constituting the fluorine gas generationdevice 100.

FIG. 2 is a block diagram showing a part of a control system in thefluorine gas generation device 100 in FIG. 1. As shown in FIG. 2, thecontrol device 90 receives an output signal from the liquid level sensor40 disposed in the anode chamber 4. This output signal indicates whetherthe liquid level of the electrolytic bath 5 in the anode chamber 4 ishigher than a predetermined liquid level (hereinafter, referred to asthe “reference level”). The control device 90 controls the invertercircuit 22I on the basis of the output signal from the liquid levelsensor 40.

More specifically, in the case where the liquid level of theelectrolytic bath 5 in the anode chamber 4 is higher than the referencelevel, the control device 90 increases the frequency of the drivingvoltage, generated in the inverter circuit 22I, by a prescribed value(of not less than 10 Hz and not more than 20 Hz, for example). Thisincreases the rotational speed of the motor 22M included in thecompressor 22, and shortens the cycle of expansion and contraction ofthe bellows, and accordingly, the discharge pressure of the hydrogen gasdischarged from the compressor 22 increases, and the pressure inside thecathode chamber 3 decreases. As a result, the liquid level of theelectrolytic bath 5 in the cathode chamber 3 rises, and the liquid levelof the electrolytic bath 5 in the anode chamber 4 falls below thereference level.

On the other hand, in the case where the liquid level of theelectrolytic bath 5 in the anode chamber 4 is not higher than thereference level, the control device 90 refrains from increasing thefrequency of the driving voltage of the compressor 22, generated in theinverter circuit 22I, by the prescribed value described above.

In this manner, when the liquid level of the electrolytic bath 5 in theanode chamber 4 rises beyond the reference level, the control device 90controls the inverter circuit 22I such that the liquid level falls tothe reference level or below.

In the following description, the control of the inverter circuit 22Ibased on the output signal from the liquid level sensor 40 performed bythe control device 90 will be referred to as “liquid level control.”

While the description was made above about the case where the liquidlevel control is performed by changing the frequency of the drivingvoltage generated in the inverter circuit 22I, the liquid level controlmay be performed by changing an effective value of the driving voltagegenerated in the inverter circuit 22I. In this case, the dischargepressure of the hydrogen gas discharged from the compressor 22 iscontrolled in accordance with a change in the amount ofexpansion/contraction of the bellows, whereby the pressure inside thecathode chamber 3 is changed. As a result, the liquid level of theelectrolytic bath 5 in the cathode chamber 3 changes, and the liquidlevel in the anode chamber 4 is adjusted.

The liquid level control may also be performed by changing both of theeffective value and frequency of the driving voltage generated in theinverter circuit 22I. As the amount of expansion/contraction and thecycle of expansion and contraction of the bellows change, the dischargepressure of the hydrogen gas discharged from the compressor 22 iscontrolled, so that the pressure inside the cathode chamber 3 ischanged. As a result, the liquid level of the electrolytic bath 5 in thecathode chamber 3 changes, and the liquid level in the anode chamber 4is adjusted.

The control device 90 also receives an output signal from the pressuregauge PS1 disposed in the cathode chamber 3. The control device 90controls at least one of the effective value and frequency of thedriving voltage generated in the inverter circuit 22I on the basis ofthe output signal from the pressure gauge PS1. As a result, the pressureinside the cathode chamber 3 is adjusted.

For example, in the case where the value of the pressure inside thecathode chamber 3 (hereinafter, referred to as the “cathode chamberpressure value”) measured by the pressure gauge PS1 at the time ofelectrolysis of HF does not agree with a prescribed value (targetpressure value), the control device 90 controls the inverter circuit 22Isuch that the difference between the cathode chamber pressure value andthe target pressure value decreases. It is noted that the targetpressure value is set, for example, to 100 kPa in absolute pressure.

Furthermore, the control device 90 receives an output signal from thepressure gauge PS2 disposed in the anode chamber 4. The control device90 controls at least one of an effective value and a frequency of thedriving voltage generated in the inverter circuit 32I on the basis ofthe output signal from the pressure gauge PS2. As a result, the pressureinside the anode chamber 4 is adjusted.

For example, in the case where the value of the pressure inside theanode chamber 4 (hereinafter, referred to as the “anode chamber pressurevalue”) measured by the pressure gauge PS2 at the time of electrolysisof HF does not agree with a prescribed value (target pressure value),the control device 90 controls the inverter circuit 32I such that thedifference between the anode chamber pressure value and the targetpressure value decreases. It is noted that the target pressure value isset, for example, to 100 kPa in absolute pressure.

In the following description, the control of the inverter circuits 22I,32I based on the output signals from the pressure gauges PS1, PS2performed by the control device 90 will be referred to as “pressurecontrol.”

The control device 90 opens the control valves 21, 23, 31, 33 whileelectrolysis of HF is taking place, whereas the control device 90 closesthe control valves 21, 23, 31, 33 while no electrolysis of HF is takingplace. This prevents the hydrogen gas or the fluorine gas downstream ofthe compressor 22, 32 from being sucked into the cathode chamber 3 orthe anode chamber 4 while no electrolysis of HF is taking place. Thecontrol device 90 also controls the opening/closing of the control valve13.

As described above, in this fluorine gas generation device 100, in thecase where the liquid level of the electrolytic bath 5 in the anodechamber 4 becomes higher than the reference level, the inverter circuit22I is controlled such that the liquid level falls to the referencelevel or below, for the following reason.

In the case of conducting electrolysis of HF in the electrolyzer 1 shownin FIG. 1, the liquid level of the electrolytic bath 5 in the anodechamber 4 is likely to rise compared to the liquid level of theelectrolytic bath 5 in the cathode chamber 3. Therefore, in the presentembodiment, the inverter circuit 22I is controlled on the basis of theoutput signal from the liquid level sensor 40 such that, when the liquidlevel of the electrolytic bath 5 in the anode chamber 4 has risen beyondthe reference level, the liquid level is adjusted to fall to thereference level or below, for restricting the fluctuations in liquidlevel.

In the liquid level control, the inverter circuit 22I is controlled, forthe following reason.

As previously described, in the fluorine gas generation device 100 inFIG. 1, the fluorine gas discharged from the anode chamber 4 is suppliedthrough the fluorine gas discharge pipe 30 to the manufacturing line ina factory or the like at a predetermined flow rate. Therefore, it ispreferable that the discharge pressure of the fluorine gas dischargedfrom the compressor 32 is maintained approximately constant.

Therefore, in the present embodiment, the inverter circuit 22I iscontrolled so as to change the discharge pressure of the compressor 22disposed on the hydrogen gas discharge pipe 20. This allows the liquidlevel of the electrolytic bath 5 in the anode chamber 4 to be adjustedto the reference level or below, without causing large fluctuations inthe flow rate of the fluorine gas discharged from the fluorine gasdischarge pipe 30.

(3) Specific Examples of Liquid Level Control and Pressure Control

FIG. 3 shows graphs illustrating specific examples of the liquid levelcontrol and the pressure control. FIG. 3( a) shows the rotational speedsof the motors 22M, 32M when the liquid level control and the pressurecontrol are carried out. In FIG. 3( a), the vertical axis representsrotational speed, and the horizontal axis represents time. Further, thebold solid line represents the rotational speed of the motor 22M, andthe long dashed dotted line represents the rotational speed of the motor32M.

Further, FIG. 3( b) shows the cathode chamber pressure value and theanode chamber pressure value when the liquid level control and thepressure control are carried out. In FIG. 3( b), the vertical axisrepresents pressure, and the horizontal axis represents time. Further,the bold broken line represents the cathode chamber pressure value, andthe solid line represents the anode chamber pressure value.

At time t0, electrolysis of HF is initiated, with the liquid level ofthe electrolytic bath 5 in the anode chamber 4 being not higher than thereference level. In the case where the liquid level of the electrolyticbath 5 is maintained at the reference level or below from time t0 totime t1, the control device 90 controls the inverter circuits 22I, 32Ion the basis of the output signals from the pressure gauges PS1, PS2(FIG. 1) (pressure control).

As such, as shown in FIG. 3( a), during the period PP in which theliquid level of the electrolytic bath 5 is not higher than the referencelevel, the inverter circuits 22I, 32I are controlled in accordance withthe fluctuations of the cathode chamber pressure value and the anodechamber pressure value, which results in gradual changes of therotational speeds of the motors 22M, 32M. In this manner, the pressureinside the cathode chamber 3 and the pressure inside the anode chamber 4are both adjusted to approach a target pressure value U.

In the case where the liquid level of the electrolytic bath 5 continuesto be higher than the reference level from time t1 to time t2, duringthis period LP, the frequency of the driving voltage of the compressor22, generated in the inverter circuit 22I, is maintained at a valueincreased by a prescribed value T with respect to the frequency at timet1 (liquid level control). This causes the liquid level of theelectrolytic bath 5 to be adjusted to fall to the reference level orbelow. It is noted that the prescribed value T is set to the order ofnot less than 5 Hz and not more than 15 Hz, for example.

At time t2, when the liquid level of the electrolytic bath 5 falls tothe reference level or below, the frequency of the driving voltage,generated in the inverter circuit 22I, is decreased by the prescribedvalue T with respect to the frequency at that time t2. As a result, asshown in FIG. 3( a), the rotational speed of the motor 22M steeply dropsby the prescribed value T from time t2, so that it becomes approximatelythe same as the rotational speed at the start point (time t1) of thatperiod LP.

In the example shown in FIG. 3, after the time t2, the liquid levelbecomes higher than the reference level during the periods from time t3to time t4, from time t5 to time t6, and from time t7 to time t8. Ineach of these periods LP as well, the frequency of the driving voltagegenerated in the inverter circuit 22I is maintained at a level increasedby the prescribed value T with respect to the frequency at the startpoint (time t3, t5, t7) of each period LP (liquid level control). Inthis manner, the liquid level of the electrolytic bath 5 is adjusted tofall to the reference level or below.

It is noted that during the periods LP described above, the controldevice 90 continues to control the inverter circuit 32I on the basis ofthe output signals from the pressure gauge PS2 (FIG. 1) (pressurecontrol). Thus, as shown in FIG. 3( a), the rotational speed of themotor 32M shows gradual changes during the periods LP as well.

As in the period PP from time t0 to time t1, in each of the periods PPfrom time t2 to time t3, from time t4 to time t5, and from time t6 totime t7 where the liquid level of the electrolytic bath 5 in the anodechamber 4 is not higher than the reference level, the inverter circuits22I, 32I are controlled in accordance with the fluctuations of thecathode chamber pressure value and the anode chamber pressure value. Asa result, as shown in FIG. 3( b), in each period PP, the cathode chamberpressure value gradually approaches the target pressure value U, and theanode chamber pressure value also gradually approaches the targetpressure value U.

As described above, by the liquid level control and the pressure controlperformed by the control device 90, the fluctuations in liquid level ofthe electrolytic bath 5 are restricted and, at the same time, thefluctuations in pressure inside the cathode chamber 3 and the anodechamber 4 are restricted.

(4) Control Flow

FIGS. 4 and 5 show a flowchart illustrating a series of processes ofelectrolysis using the liquid level control and the pressure control. Inthe following, the control of the inverter circuit 22I by the controldevice 90 will be described. In the initial state, the compressors 22,32 are operating at prescribed rotational speeds in advance.

First, when the start of electrolysis of HF is instructed by an inputdevice (not shown) or the like, the control device 90 applies aprescribed voltage across the cathode 6 and the anode 7 (step S1), andopens two control valves 21, 23 disposed on the hydrogen gas dischargepipe 20 (step S2).

Next, the control device 90 determines, on the basis of the outputsignal from the liquid level sensor 40, whether the liquid level of theelectrolytic bath 5 in the anode chamber 4 is higher than a referencelevel (step S3).

If the liquid level is higher than the reference level, the controldevice 90 controls the inverter circuit 22I to increase the rotationalspeed of the motor 22M by a prescribed value T (step S4). For example,the control device 90 increases the frequency of the driving voltage ofthe compressor 22, generated in the inverter circuit 22I, by aprescribed value from the current frequency, to thereby increase therotational speed of the motor 22M by the prescribed value T.

The control device 90 then determines, on the basis of the output signalfrom the liquid level sensor 40, whether the liquid level of theelectrolytic bath 5 in the anode chamber 4 is higher than the referencelevel (step S5). This step is repeated until the liquid level falls tothe reference level or below. Thereafter, when the liquid level becomesnot higher than the reference level, the control device 90 controls theinverter circuit 22I to decrease the rotational speed of the motor 22Mby the prescribed value T (step S6). The process then returns to stepS3.

If it is determined in step S3 that the liquid level is not higher thanthe reference level, the control device 90 acquires a cathode chamberpressure value measured by the pressure gauge PS1 (step S7).

Here, in the control device 90, a target pressure value U for thecathode chamber 3 is stored in advance. The target pressure value U isset, for example, by an operator through manipulation of an input deviceor the like.

The control device 90 determines whether the acquired cathode chamberpressure value agrees with the preset target pressure value U (step S8).

If the cathode chamber pressure value agrees with the target pressurevalue U, the control device 90 controls the inverter circuit 22I in FIG.2 to maintain the rotational speed of the motor 22M at the current value(step S9). For example, the control device 90 maintains the frequency ofthe driving voltage generated in the inverter circuit 22I at the currentvalue, to thereby maintain the rotational speed of the motor 22M.

If the cathode chamber pressure value does not agree with the targetpressure value U, the control device 90 changes the rotational speed ofthe motor 22M by controlling the inverter circuit 22I such that thedifference between the cathode chamber pressure value and the targetpressure value U decreases (step S10). For example, the control device90 changes the frequency of the driving voltage generated in theinverter circuit 22I from the current value such that the differencebetween the cathode chamber pressure value and the target pressure valueU decreases, to thereby change the rotational speed of the motor 22M.

For example, in the case where the cathode chamber pressure value islower than the target pressure value U, the control device 90 controlsthe inverter circuit 22I such that the driving voltage applied to themotor 22M decreases. This reduces the rotational speed of the motor 22M,and decreases the discharge pressure of the compressor 22. As a result,the cathode chamber pressure value increases to approach the targetpressure value U, whereby the difference between the cathode chamberpressure value and the target pressure value U decreases.

Conversely, in the case where the cathode chamber pressure value ishigher than the target pressure value U, the control device 90 controlsthe inverter circuit 22I such that the driving voltage applied to themotor 22M increases. This increases the rotational speed of the motor22M, and increases the discharge pressure of the compressor 22. As aresult, the cathode chamber pressure value decreases to approach thetarget pressure value U, whereby the difference between the anodechamber pressure value and the target pressure value U decreases.

After the processing in step S9 or S10, the control device 90 determineswhether an end of the electrolysis of HF has been instructed by an inputdevice or the like (step S11). If the end of electrolysis has not beeninstructed, the control device 90 returns to the processing in step S3.On the other hand, if the end of electrolysis has been instructed, thecontrol device 90 stops applying the voltage across the cathode 6 andthe anode 7 (step S12), and closes the two control valves 21, 23disposed on the hydrogen gas discharge pipe 20 (step S13). Thisterminates the electrolysis of HF.

In the flowchart in FIGS. 4 and 5, the processing in steps S3 through S6corresponds to the above-described liquid level control, and theprocessing in steps S7 through S10 corresponds to the above-describedpressure control.

While the control of the inverter circuit 22I by the control device 90has been described above, when the electrolysis of HF is started, thecontrol device 90 controls the inverter circuit 32I similarly as in theabove-described processing in steps S7 through S10.

(5) Effects

(5-a) In this fluorine gas generation device 100, the control device 90carries out the liquid level control. Therefore, even when the liquidlevel of the electrolytic bath 5 in the anode chamber 4 becomes higherthan the reference level, the liquid level is adjusted to fall to thereference level or below. The fluctuations in liquid level of theelectrolytic bath 5 are restricted in this manner.

Further, the liquid level control is adjusted by changing the rotationalspeed of the motor 22M of the compressor 22. This eliminates the need toadjust the discharge pressure of the hydrogen gas in the hydrogen gasdischarge pipe 20 through the operations of opening/closing the controlvalves 21, 23, 31, 33. It is thus unnecessary to perform maintenance dueto the early deterioration of the control valves 21, 23, 31, 33, and thenumber of times of maintenance work decreases. This results in areduction of the maintenance cost of the fluorine gas generation device100.

(5-b) Further, in this fluorine gas generation device 100, the controldevice 90 carries out the pressure control in addition to the liquidlevel control. This restricts the fluctuations in pressure inside thecathode chamber 3 and the anode chamber 4, while restricting thefluctuations in liquid level of the electrolytic bath 5. As a result,the fluctuations in electrolysis conditions upon electrolysis of HF arerestricted.

(5-c) The liquid level control and the pressure control are carried outby changing the rotational speed of the motor 22M by controlling theinverter circuits 22I, 32I. Accordingly, compared to the case ofopening/closing the control valves 21, 23, 31, 33, the dischargepressure of the hydrogen gas in the hydrogen gas discharge pipe 20 andthe discharge pressure of the fluorine gas in the fluorine gas dischargepipe 30 can be adjusted readily and finely. Therefore, even if theelectrolyzer 1 is reduced in size, the pressure in each chamber 3, 4 canbe controlled with ease and with precision. This enables downsizing ofthe fluorine gas generation device 100.

(6) Other Embodiments

(6-a) In the above embodiment, the description was made about the caseof setting a common target pressure value U for the cathode chamberpressure value and the anode chamber pressure value for performing thepressure control. Not limited thereto, the target pressure value (firsttarget pressure value) set for the cathode chamber pressure value andthe target pressure value (second target pressure value) set for theanode chamber pressure value may differ from each other. In this case,for example, the second target pressure value is preferably set smallerthan the first target pressure value.

Thus, by the pressure control, the cathode chamber pressure value isadjusted to approach the first target pressure value, and the anodechamber pressure value is adjusted to approach the second targetpressure value that is smaller than the first target pressure value.Consequently, the pressure inside the cathode chamber 3 becomes higherthan the pressure inside the anode chamber 4. This prevents the liquidlevel of the electrolytic bath 5 in the cathode chamber 3 from risingbeyond the liquid level of the electrolytic bath 5 in the anode chamber4.

For example, the first target pressure value is set to 100 kPa inabsolute pressure, and the second target pressure value is set to notless than 95 kPa and not more than 99 kPa in absolute pressure.

It is noted that the first and second target pressure values may be setas appropriate in accordance with the volumetric capacities of thecathode chamber 3 and the anode chamber 4.

(6-b) As described above, in the fluorine gas generation device 100 inFIG. 1, the liquid level sensor 40 for detecting the liquid level of theelectrolytic bath 5 is disposed in the anode chamber 4. The controldevice 90 carries out the liquid level control on the basis of theoutput signal from the liquid level sensor 40.

Not limited thereto, in the case where the flow rate of the fluorine gasdischarged from the fluorine gas discharge pipe 30 is not particularlydetermined, the liquid level sensor 40 may be disposed in the cathodechamber 3. Further, the control device 90 may carry out the liquid levelcontrol on the basis of the output signal from the liquid level sensor40 disposed in the cathode chamber 3.

FIG. 6 is a schematic diagram showing the configuration of the fluorinegas generation device according to another embodiment. In the following,the differences of the fluorine gas generation device 100 in FIG. 6 fromthe fluorine gas generation device 100 in FIG. 1 will be described.

As shown in FIG. 6, in this fluorine gas generation device 100, theliquid level sensor 40 is not disposed in the anode chamber 4, butdisposed in the cathode chamber 3. In the present example, the controldevice 90 controls the inverter circuit 32I on the basis of the outputsignal from the liquid level sensor 40 (liquid level control).

For example, in the case where the liquid level of the electrolytic bath5 in the cathode chamber 3 has become higher than the reference level,the control device 90 causes the frequency of the driving voltagegenerated in the inverter circuit 32I to be increased by a prescribedvalue with respect to the frequency at that time point. This increasesthe rotational speed of the motor 32M included in the compressor 32, andincreases the discharge pressure of the fluorine gas discharged from thecompressor 32, whereby the pressure inside the anode chamber 4decreases. As a result, the liquid level of the electrolytic bath 5 inthe anode chamber 4 rises, and also, the liquid level of theelectrolytic bath 5 in the cathode chamber 3 falls below the referencelevel.

In this manner, even when the liquid level of the electrolytic bath 5 inthe cathode chamber 3 becomes higher than the reference level, theliquid level control is carried out on the basis of the output signalfrom the liquid level sensor 40, so that the liquid level is adjusted tofall to the reference level or below.

(6-c) Not limited to the fluorine gas generation devices 100 in FIGS. 1and 6, the liquid level sensor 40 may be provided in each of the cathodechamber 3 and the anode chamber 4. The control device 90 may carry outthe liquid level control on the basis of the output signals from theliquid level sensors 40 disposed in the cathode chamber 3 and the anodechamber 4.

FIG. 7 is a schematic diagram showing the configuration of the fluorinegas generation device according to yet another embodiment. In thefluorine gas generation device 100 in FIG. 7, a liquid level sensor 40is disposed in each of the cathode chamber 3 and the anode chamber 4. Inthe present example, the control device 90 controls the invertercircuits 22I, 32I on the basis of the output signals from the respectiveliquid level sensors 40 (liquid level control).

In this manner, even when the liquid level of the electrolytic bath 5 inthe cathode chamber 3 becomes higher than the reference level, theliquid level is adjusted to fall to the reference level or below.Further, even when the liquid level of the electrolytic bath 5 in theanode chamber 4 becomes higher than the reference level, the liquidlevel is adjusted to fall to the reference level or below. It is thuspossible to restrict the fluctuations in liquid level of theelectrolytic bath 5 in the cathode chamber 3 and the anode chamber 4.

(7) Correspondences between the Elements Recited in the Claims and ThoseDescribed in the Embodiments

In the following paragraphs, non-limiting examples of correspondencesbetween various elements recited in the claims below and those describedabove with respect to various preferred embodiments of the presentinvention are explained.

In the embodiments described above, the hydrogen gas is an example ofthe first gas, the fluorine gas is an example of the second gas, thecathode chamber 3 is an example of the first chamber, the anode chamber4 is an example of the second chamber, the hydrogen gas discharge pipe20 is an example of the first gas discharge path, and the fluorine gasdischarge pipe 30 is an example of the second gas discharge path.

Further, the liquid level sensor 40 is an example of the liquid leveldetector, the compressor 22 is an example of the first pump, the motor22M is an example of the motor of the first pump, the inverter circuit22I is an example of the first inverter circuit, and the pressure gaugePS1 is an example of the first pressure detector.

Furthermore, the compressor 32 is an example of the second pump, themotor 32M is an example of the motor of the second pump, the invertercircuit 32I is an example of the second inverter circuit, and thepressure gauge PS2 is an example of the second pressure detector.

Further, the control device 90 is an example of the controller, thecontrol valves 21, 23 are examples of the first open/close valve, andthe control valves 31, 34 are examples of the second open/close valve.

Furthermore, the target pressure value U is an example of the first andsecond target values, the first target pressure value is an example ofthe first target value, and the second target pressure value is anexample of the second target value.

As the elements recited in the claims, a variety of other elementshaving the configuration or function recited in the claims may be usedas well.

INDUSTRIAL APPLICABILITY

The present invention is applicable to the generation of gases byelectrolysis.

1. A gas generation device that generates a first gas and a second gasby electrolysis, comprising: an electrolyzer divided into a firstchamber and a second chamber and containing therein an electrolytic bathincluding a compound to be electrolyzed; a first gas discharge paththrough which the first gas generated in said first chamber isdischarged; a second gas discharge path through which the second gasgenerated in said second chamber is discharged; a liquid level detectorthat detects a liquid level of the electrolytic bath in said secondchamber; a first pump having a motor and provided on said first gasdischarge path; a first inverter circuit that generates a drivingvoltage to be applied to the motor of said first pump; and a controllerthat controls said first inverter circuit, in the case where the liquidlevel detected by said liquid level detector is higher than apredetermined reference level, such that at least one of an effectivevalue and a frequency of the driving voltage being applied to the motorof said first pump increases.
 2. The gas generation device according toclaim 1, further comprising a first pressure detector that detects apressure inside said first chamber, wherein in the case where the liquidlevel detected by said liquid level detector is not higher than saidreference level, said controller controls at least one of an effectivevalue and a frequency of the driving voltage generated by said firstinverter circuit such that the pressure detected by said first pressuredetector approaches a first target value.
 3. The gas generation deviceaccording to claim 1, further comprising: a second pump having a motorand provided on said second gas discharge path; a second invertercircuit that generates a driving voltage to be applied to the motor ofsaid second pump; and a second pressure detector that detects a pressureinside said second chamber, wherein said controller controls at leastone of an effective value and a frequency of the driving voltagegenerated by said second inverter circuit such that the pressuredetected by said second pressure detector approaches a second targetvalue.
 4. The gas generation device according to claim 1, furthercomprising: a first pressure detector that detects a pressure insidesaid first chamber; a second pump having a motor and provided on saidsecond gas discharge path; a second inverter circuit that generates adriving voltage to be applied to the motor of said second pump; and asecond pressure detector that detects a pressure inside said secondchamber, wherein in the case where the liquid level detected by saidliquid level detector is not higher than said reference level, saidcontroller controls at least one of an effective value and a frequencyof the driving voltage generated by said first inverter circuit suchthat the pressure detected by said first pressure detector approaches afirst target value, and also controls at least one of an effective valueand a frequency of the driving voltage generated by said second invertercircuit such that the pressure detected by said second pressure detectorapproaches a second target value that is smaller than said first targetvalue.
 5. The gas generation device according to claim 1, furthercomprising: a first open/close valve provided on said first gasdischarge path; and a second open/close valve provided on said secondgas discharge path, wherein said controller opens said first and secondopen/close valves in the case where electrolysis is carried out in saidelectrolyzer, and closes said first and second open/close valves in thecase where no electrolysis is carried out in said electrolyzer.
 6. Thegas generation device according to claim 1, wherein said first chamberis a cathode chamber, and said second chamber is an anode chamber. 7.The gas generation device according to claim 1, wherein said second gasis fluorine.
 8. A gas generation method for generating a first gas and asecond gas by electrolysis by using an electrolyzer divided into a firstchamber and a second chamber, the method comprising the steps of:generating the first and second gases in said first and second chambers,respectively, by applying a voltage to an electrolytic bath contained insaid electrolyzer, and discharging the first and second gases generatedin said first and second chambers through first and second gas dischargepaths, respectively; controlling, by a first pump having a motor, thedischarge of the first gas through said first gas discharge path;detecting a liquid level of the electrolytic bath in said secondchamber; applying a driving voltage to the motor of said first pump by afirst inverter circuit; and in the case where said detected liquid levelis higher than a predetermined reference level, controlling said firstinverter circuit such that at least one of an effective value and afrequency of the driving voltage being applied to the motor of saidfirst pump increases.
 9. The gas generation method according to claim 8,further comprising the steps of: detecting a pressure inside said firstchamber; in the case where said detected liquid level is not higher thanthe predetermined reference level, controlling at least one of aneffective value and a frequency of the driving voltage generated by saidfirst inverter circuit such that said detected pressure inside saidfirst chamber approaches a first target value; controlling, by a secondpump having a motor, the discharge of the second gas through said secondgas discharge path; applying a driving voltage to the motor of saidsecond pump by a second inverter circuit; detecting a pressure insidesaid second chamber; and controlling at least one of an effective valueand a frequency of the driving voltage generated by said second invertercircuit such that said detected pressure inside said second chamberapproaches a second target value that is smaller than said first targetvalue.